Batteries are electrochemical devices that store and release electrical energy through reversible chemical reactions. They consist of one or more electrochemical cells, each containing positive and negative electrodes separated by an electrolyte. When a battery is charged, electrons flow from the power source through the electrodes, causing chemical reactions that store energy. During discharge, the stored energy is released as electrons flow in the opposite direction. Batteries come in various types, including lead-acid, lithium-ion, nickel-cadmium, and more, each with different characteristics in terms of energy density, power output, cycle life, and cost. Lithium-ion batteries, for example, have become popular due to their high energy density, longer cycle life, and relatively low self-discharge rate, making them suitable for portable electronics, electric vehicles, and grid energy storage.
On the other hand, capacitors store electrical energy in an electric field formed between two conductive plates separated by an insulating material, known as a dielectric. When a voltage is applied across the plates, electrons accumulate on one plate, while an equal number of electrons are depleted from the other plate, resulting in the formation of an electric field. Unlike batteries, capacitors store energy through the separation of charges without involving chemical reactions. Capacitors are known for their ability to rapidly charge and discharge, making them useful for applications that require high power output, such as in camera flashes, electric power tools, and regenerative braking systems in electric vehicles. However, capacitors generally have lower energy density compared to batteries and cannot store as much energy for a given size and weight.
Both batteries and capacitors have their advantages and limitations, and researchers are continuously working to improve their performance and address their drawbacks. The demand for electrical energy storage has surged in recent years with the increasing integration of renewable energy sources like solar and wind power, which are intermittent in nature. Energy storage systems help mitigate the fluctuations in power generation and enable the utilisation of renewable energy when the demand is high or when the renewable source is unavailable.
The development of advanced battery chemistry, such as solid-state batteries, and the exploration of alternative materials for capacitors, such as super-capacitors based on carbon nano-tubes or graphene, are ongoing research areas. These innovations aim to enhance energy density, power density, cycle life, safety, and sustainability while reducing costs. Furthermore, the integration of batteries and capacitors in hybrid energy storage systems can leverage their complementary characteristics to optimise overall performance.
